The present invention relates generally to ball screws and ball nuts, and more particularly to a ball-nut assembly having a crossover member and to a method for making a ball-nut assembly having a crossover member.
Conventional automotive braking systems include those which use a ball-screw-and-ball-nut assembly, wherein the brake booster serves as a housing, wherein the ball screw is turned by a gear driven by an electric brake caliper motor, wherein the ball nut is connected to the brake pad, and wherein rotation of the ball screw axially moves the ball nut. In some known ball-nut assemblies, an exterior tube extending above the ball nut serves as a crossover for the balls, as is known to the artisan. However, such exterior tubes demand close part tolerances which are expensive and difficult to achieve. Also, such protruding exterior tubes are not suitable for certain applications such as being housed in a brake caliper housing. In other known ball-nut assemblies, an internal crossover member is used which is inserted into a radial through slot of the ball nut from inside the ball nut, which abuts a radially-inward-facing ledge of the ball nut surrounding the through slot, and which floats while being captured between the ball screw and the ball nut as is known to the artisan. Such internal crossovers are suitable for many applications including being housed in an automotive brake booster. However, such internal crossovers demand close part tolerances which are expensive and difficult to achieve. If close tolerances are not achieved, the ball screw and ball nut assembly will not work as is known to the artisan.
What is needed is a ball-nut assembly, and a method for making a ball nut assembly, which uses an internal crossover member but which does not require close part tolerances to ensure proper operation of a ball-screw-and-ball-nut assembly.
A first expression of a first embodiment of the invention is for a ball-nut assembly including a ball nut and a crossover member. The ball nut includes a radial through slot and includes an outer surface having a first portion, having a ledge radially recessed from the first portion and at least partially bounding the through slot, and having an undercut wall connecting the ledge and the first portion. The crossover member has a flange supported by the ledge and has a crossover-grooved portion positioned in the through slot, wherein the flange has at least one deformed portion contacting the undercut wall of the outer surface of the ball nut.
A second expression of a first embodiment of the invention is for a ball-screw-and-ball-nut assembly including a ball nut, a crossover member, a ball screw and balls. The ball nut includes an inside helical groove, includes a radial through slot, and includes an outer surface having a first portion, having a ledge radially recessed from the first portion and at least partially bounding the through slot, and having an undercut wall connecting the ledge and the first portion. The crossover member has a flange supported by the ledge and has a crossover-grooved portion positioned in the through slot, wherein the flange has at least one deformed portion contacting the undercut wall of the outer surface of the ball nut. The ball screw includes an outside helical groove and is positioned inside the ball nut. The balls contact the crossover-grooved portion of the crossover member and a portion of the inside and outside helical grooves.
A first method of the invention is for making a ball-nut assembly and includes steps a) through d). Step a) includes obtaining a ball nut including a radial through slot and including an outer surface having a first portion, having a ledge radially recessed from the first portion and at least partially bounding the through slot, and having an undercut wall connecting the ledge and the first portion. Step b) includes obtaining a crossover member having a flange and a crossover-grooved portion. Step c) includes positioning the crossover member from outside the ball nut to have the flange supported by the ledge and the crossover-grooved portion disposed in the through slot. Step d) includes deforming the flange creating a staked portion of the flange which contacts the undercut wall of the outer surface of the ball nut. In one example, the first method also includes after step a) and before step c) the step on aligning the ball nut on a locating arbor which simulates balls placed around a ball screw and wherein step c) includes aligning the crossover member on the locating arbor and step d) includes using a stake punch.
Several benefits and advantages are derived from one or more of the first method and the first and second expressions of a first embodiment of the invention. The example which includes the locating arbor, which simulates balls placed around a ball screw for proper alignment of the crossover member on the ball nut, enables close assembly tolerances for inexpensive components that can be manufactured with loose part tolerances, as can be appreciated by those skilled in the art. Once properly aligned, the example which includes the stake punch deforms and stakes the crossover member to the undercut wall of the ball nut to maintain the crossover member in proper aligned attachment to the ball nut for smooth operation of a ball-screw-and-ball-nut assembly.